I was running 0.9.3 for a long time, waiting for 1.0 to arrive. I updated from 0.9.3 to 1.0 (as it said I could).
It ran fine for the first 4-5 days, then I clicked CHECK FOR UPDATES and it completely barfed without warning. Luckily I was able to get into Firefox safe-mode to backup my bookups.
Uninstalled Firefox, reinstalled 1.0 No Luck.
Then I had to completely remove Firefox AND the profile folders. Re-boot PC and then install 1.0 from scratch. Then had to re-get extensions and set it back up again the way I like it.
I reckon they still have a way to go with the installers / updaters.
But I still LOVE LOVE LOVE FireFox.